This section provides background information related to the present disclosure which is not necessarily prior art.
A vehicle, such as a snowmobile, generally includes an engine assembly. The engine assembly is operated with the use of fuel to generate power to drive the vehicle. The power to drive a snowmobile is generally generated by a combustion engine that drives pistons and a connected crankshaft. Two-stroke snowmobile engines are highly tuned, and high specific power output engines that operate under a wide variety of conditions.
The modern two-stroke snowmobile engine must be able to operate at peak performance in ambient air temperatures of −40 to 100 F and from sea level to 12000 ft in elevation. Consumer expectations of snowmobile engines, especially two-stroke engines have increased substantially as customer's desire increased engine life and improved run quality compared to previous generations of snowmobiles.
The range of fuel octane and ethanol content combinations have created a new set of challenges in the development and calibration of 2-stroke snowmobile engines. During previous generations of snowmobile engines, the most common fuels encountered by customers was 91 octane with no ethanol (91E0) and 87 octane with 10% ethanol (87E10). However, over the last several years, the presence of 91 octane with 10% ethanol (91E10) has increased significantly, as has the proliferation of 5-7% ethanol blends of all octane levels. Each of these octane and ethanol combination creates slightly different calibration requirements; for example, 87E10 requires both ignition retard and a fuel increase compared to a 91E0. A calibration optimized for 91E0 will see increased detonation and/or power limiting control when run on 87E10 whereas an 87E10 optimized calibration will suffer poor performance when run on 91E0 fuel. The 91E10 and 5-7% ethanol blends complicates matter further as the fueling requirements fall in between the 91E0 and 87E10 boundaries.
To alleviate the difference in calibration needed between a 91E0 and 87E10 fuel, Polaris snowmobiles feature a fuel setting mode done through the vehicle gauge. This fuel setting mode applies an ignition and fuel offset to certain RPM and TPS brake points to accommodate the different fuel types. However, since this setting is user controlled, there is potential for the user to select the wrong fuel setting. This happens can happen in two ways; the first being the user selecting the premium/non ethanol (91E0) setting thinking they are getting maximum performance while the second is the user selecting the non-premium/ethanol (87E0) setting thinking they are doing everything they can to protect the engine, at the expense of performance. However, testing has shown that using the wrong fuel setting can lead to performance and durability problems.